High-strength bolts are made of high-strength materials. The screws, nuts and washers of high-strength bolts are all made of high-strength titanium and steel. Ordinary bolts are usually made of Q235 steel.

From the perspective of intensity level:

High-strength bolts are increasingly used. Two strength levels of 8.8s and 10.9s are commonly used, of which 10.9 is the majority. The strength grade of ordinary bolts is lower, generally 4.4, 4.8, 5.6 and 8.8.

From the perspective of force characteristics:

High-strength bolts exert pre-tension and transmit external force by friction. Ordinary bolt connections rely on the shear resistance of the bolt rod and the pressure of the hole wall to transmit the shear force. The pretension generated when the nut is tightened is small, and its effect can be ignored. In addition to its high material strength, high-strength bolts also impose a large amount on the bolt. The pre-tension force produces an extrusion force between the connecting members, so that there is a great friction force perpendicular to the screw direction, and the pre-tension force, the anti-slip coefficient and the type of steel directly affect the bearing capacity of the high-strength bolt.

According to the characteristics of the force, it is divided into pressure type and friction type. The calculation methods of the two are different. The minimum specification of high-strength bolts is M12, and commonly used are M16~M30. The performance of oversized bolts is unstable and should be used with caution in design.

The difference between high-strength bolt friction type and pressure type connection:

The high-strength bolt connection is to clamp the plates of the connecting plate through the large tightening pretension in the bolt rod, which is sufficient to generate a large friction force, thereby improving the integrity and rigidity of the connection. When subjected to shear force, according to the design and The different force requirements can be divided into high-strength bolt friction type connection and high-strength bolt pressure-bearing type connection. The essential difference between the two is that the limit state is different. Although they are the same type of bolts, they are calculated in terms of calculation methods, requirements, and scope of application All are very different.

In the shear design, the high-strength bolt friction type connection is the limit state when the external shear force reaches the maximum possible friction force provided by the bolt tightening force between the contact surfaces of the plate, which is to ensure that the internal and external shear force of the connection does not exceed during the entire period of use. Maximum friction. The plates will not undergo relative sliding deformation (the original gap between the screw and the hole wall is always maintained), and the connected plates will be stressed as a whole according to the elasticity. In the shear design, the external shear force is allowed to exceed the maximum friction force in the high-strength bolt pressure-bearing connection. At this time, relative sliding deformation occurs between the connected plates until the bolt rod contacts the hole wall, and then the connection depends on the bolt rod Shaft shear and hole wall pressure and the friction between the contact surfaces of the plate jointly transmit force, and finally the shaft shear or hole wall pressure failure is regarded as the limit state of connection shear. In short, friction-type high-strength bolts and pressure-bearing high-strength bolts are actually the same kind of bolts, it is just whether slippage is considered in the design. Friction-type high-strength bolts must not slide, and the bolts do not bear shear force. Once slipped, the design is considered to have reached the failure state, which is technically mature; pressure-bearing high-strength bolts can slide, and the bolts also bear shear force. Bolt damage (bolt shearing or steel plate crushing).

From the perspective of usage:

The bolt connection of the main components of the building structure generally adopts high-strength bolt connection. Ordinary bolts can be reused, but high-strength bolts cannot be reused. High-strength bolts are generally used for permanent connections.

High-strength bolts are pre-stressed bolts. The friction type uses a torque wrench to apply the specified pre-stress, and the pressure-bearing type unscrews the torx head. Ordinary bolts have poor shear resistance and can be used in secondary structural parts. Ordinary bolts only need to be tightened.